Frequency inverter



FIG. 1 is a front, top and right side perspective view of a frequency inverter showing our new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a top plan elevational view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a right side elevational view thereof;

FIG. 6 is a rear elevational view thereof; and,

FIG. 7 is a rear, bottom and left side perspective view thereof. 

The ornamental design for a frequency inverter, as shown. 